Sleep-mediated axes of interaction between psychological and immune memory

Sleep is a dynamic communication interface between the nervous and immune systems, mediating their complementary homeostatic roles through memory formation. Psychological and immune memory exhibit non-coincidental parallels in their formation processes, the underlying sleep architecture involved, and their influences on one another. Considering the type of psychological memory involved, the directions of interaction and underlying physiological mechanisms linking both memory domains remain elusive. Additionally, the collaborative influence of the sleep stages in mediating these interactions in the absence of conscious awareness are understudied. Using the three-step framework of declarative memory formation, this review bridges the sleep-mediated similarities across both memory systems. It interprets how sleep-supported immune memory formation protects declarative spatial memory; a direction defined as the immune-to-declarative memory axis. Conversely, another three-facet framework reflecting the brain's evolutionary influence on immunity introduces the underexplored direction of how psychological memory may unconsciously influence immune memory retrieval; the nondeclarative-to-immune memory axis. From that, the review highlights a gap in knowledge pertaining to the predictive, associative, and integrative processes characteristic of non-declarative memory, drawing from key limbic system regions, signaling molecules, and regulatory circadian rhythm processes. It also revisits the dichotomy of non-rapid/rapid eye movement sleep, traditionally segregated to the reinforcement of declarative and non-declarative memory, respectively, arguing for an integrative role of sleep stages in modulating both types of memory and facilitating inter-memory-system influence. By identifying key gaps and proposing future directions, the review advocates for a holistic and interdisciplinary approach to understanding sleep-mediated interactions across the body's memory systems within psychoneuroimmunology.